Mechanisms of the relaxant effect of a Danshen and Gegen formulation on rat isolated cerebral basilar artery

Abstract

Aim of the study: Danshen (root of Salvia miltiorrhiza) and Gegen (root of Pueraria lobata) are two herbs used in traditional Chinese medicine, most commonly for their putative cardioprotective and anti-atherosclerotic effects. In this study, the actions of a Danshen and Gegen formulation (DG; ratio 7:3) were investigated on rat-isolated cerebral basilar artery. Materials and methods: Rat basilar artery rings were precontracted with 100nM U46619. Involvement of endothelium-dependent mechanisms was investigated by mechanical removal of the endothelium; K+ channels were investigated by pretreatment of the artery rings with various K+ channel inhibitors, and Ca2+ channels were investigated in artery rings incubated with Ca2+-free buffer and primed with 100nM U46619 for 5min prior to adding CaCl2 to elicit contraction. Results: DG produced concentration-dependent relaxation of the artery rings with an IC50 of 895±121μg/ml. Mechanical removal of the endothelium or pretreatment with the BKCa channel inhibitor iberiotoxin (100nM), the KV channel inhibitor 4-aminopyridine (1mM), or the KIR channel inhibitor barium chloride (100μM), all had no effect on the DG-induced response (P>0.05 for all). However, pretreatment with the KATP channel inhibitor glibenclamide (1μM), the non-selective K+ channel inhibitor tetraethylammonium (TEA, 100mM), or a combination of all the K+ channel inhibitors (iberiotoxin+4-aminopyrindine+barium chloride+glibenclamide+TEA) produced significant inhibition on the DG-induced response (P<0.01 for all); its maximum vasorelaxant effect (Imax) was reduced by 37, 24, and 30%, respectively. Preincubation of the artery rings with DG for 10min produced concentration-dependent (1, 3 and 7mg/ml) and total inhibition on the CaCl2-induced vasoconstriction. Conclusions: These findings suggest the vasorelaxant effect of DG on rat basilar artery is independent of endothelium-derived mediators, whereas, inhibition of Ca2+ influx in the vascular smooth muscle cells is important, and a minor component is mediated by the opening of KATP channels. DG could be a useful cerebroprotective agent in some patients with occlusive cerebrovascular disease. © 2010 Elsevier Ireland Ltd.